The overall goal is to define cellular and molecular mechanisms involved in the modulation of normal and neoplastic hematopoiesis. Studies will be pursued on the mechanism of action of erythroid-potentiating activity (EPA), the physiology of GM-CSF in humans, and the interaction of polypeptide growth hormones with normal and malignant hematopoietic cells. Radioimmunoassays will be developed for EPA and CSF. These hemopoietins have been molecularly cloned and are expressed in mammalian cells. The purified and recombinant proteins will be used to develop antibodies for the radioimmunoassays which will be applied to normals and to patients with various disorders of hematopoiesis for the purpose of defining the physiologic and pathophysiologic role of these hemopoietic regulators in man. The EPA receptor will be purified and antibodies developed against it. Its amino terminus sequence will be determined in order to construct oligonucleotide probes to molecularly clone the human gene for the EPA receptor. EPA receptor clones will be used to predict the structure and sequence of the receptor protein and to examine its organization in genomic DNA. Also, expression of receptor RNA will be studied by Northern analysis in various and malignant cell types. The interaction of specific polypeptide hormones with normal and malignant hematopoietic cells will be investigated in depth with respect to the mechanism of action of EPA at the cellular level and the action of growth hormone, insulin, and insulin growth factors on hemic cells. Permanent human T-lymphoid cell lines will be developed using the human T-leukemia viruses to transform cells from appropriate patients in order the examine the genetic or epigenetic basis of hormonal resistance and to define the underlying mechanism thereof. These studies should provide important insights regarding the role of various hemopoietins in normal and malignant hematopoiesis in man and define the basis of polypeptide growth hormone action on hemic cells.